Culture device for sampling and/or counting micro-organism

ABSTRACT

A culture device is described comprising a solid body of culture medium and supporting means for maintaining the integrity of the body of culture medium, the culture medium providing a culture surface having an endless boundary or perimeter, a body of medium protruding from and the culture surface being spaced from any aforesaid means disposed externally of the body of culture medium.

The present invention relates to a culture device for samplingmicro-organisms and/or counting micro-organisms. The present inventionalso relates to apparatus by means of which Such a culture device can beprepared.

Microbial count tests have become a useful sanitary control tool formonitoring sanitation and quality levels of food plants to ensure thatproducts are safe and wholesome. The tests involve transfer ofmicro-organisms from cleaned and sanitised test surfaces onto a cultureagar medium (CAM) which allows growth of a wide range ofmicro-organisms. After a period of incubation, each microbial celldevelops into a visible colony of cells. The number of colonies providesa measure of the number of micro-organisms on the test surface.

Various methods are available for assessment of microbiological statusof food contact surfaces in equipment such as piping, containers, tablesand conveyors which are in contact with food products. Of these methods,the rinsing, swabbing and agar contact methods have been considered assatisfactory and have gained general acceptance.

In the agar contact method a replicate organism direct agar contact(RODAC) plate is used. The RODAC plate provides a simple agar contacttool for sampling surfaces. It is useful for monitoring the sanitaryquality of surfaces used in food industries and hospitals. The RODACplate is best suited for flat smooth impervious surfaces such asceiling, wall and floor surfaces and surfaces of tables, containers andconveyors.

The RODAC plate has a rim and is filled with CAM which has a slightlyconvex surface with the centre of its meniscus rising above the rim. Thesurface of the CAM is pressed against the test surface to be sampled. Itis necessary to make good contact of the agar with the test surface.Accordingly when sampling, care has to be taken to ensure that theentire agar meniscus contacts the test surface: a rolling uniformpressure on the back of the plate to effect contact aids in achievingthis.

A disadvantage inherent in the rinsing, swabbing and agar contactmethods is that uniformity and consistency in sampling depend primarilyon the skill of persons taking the samples. Technicians need to betrained in sampling technique in order to obtain uniform and meaningfulresults.

In particular in the agar contact method the filling of the RODAC platewith CAM to achieve a slightly convex surface is a slow, cares andexacting process. Additionally it is not sufficient simply to press theCAM of the filled plate against the test surface since only that part ofthe surface of the CAM within the curved edge portion of the meniscuswould contact the test surface. This part of the surface is ofindefinite area. Thus the area of the test surface contacted would beindefinite and consequently an accurate account of microorganisms perunit area of the test surface would not be obtainable.

The present invention enables the above-mentioned disadvantage to beovercome and provides, at least in preferred embodiments, additionaladvantages.

In accordance with a first aspect of the invention, there is provided aculture device comprising a body of culture medium and supporting meansfor maintaining the integrity of the body of culture medium, the culturemedium providing a surface (referred to below as the "the culturingsurface") having a defined endless boundary or perimeter, the body ofculture medium protruding from and the culturing surface being spacedfrom any aforesaid means disposed externally of the body of culturemedium.

The endless boundary or perimeter is defined by a side surface oncontiguous side surfaces of the culture medium, which side surface orsurfaces meet the culturing surface, preferably abruptly, along anendless line or endless series of lines at an angle substantiallydiffering from 180°, preferably at an angle of 90°, so that the boundaryor perimeter is precisely defined.

The defined boundary or perimeter of the culturing surface enables itssurface area to be clearly ascertained. This enables the number ofmicro-organisms per unit area on a test surface and which have beentransferred to the culturing surface to be accurately evaluated.

The supporting means may be at least partly external to the body ofculture medium and/or may be at least partly internal to the body ofculture medium.

Thus the supporting means may be wholly external to the body of culturemedium, wholly internal of the body of culture medium or may be in partexternal to and in part internal of the body of culture medium.

The supporting means may comprise an open cell sponge or foam ormaterial having a three-dimensional reticulated structure, such as askeletal foam, or other pervious or permeable material impregnated withthe culture medium. A suitable material is like that used in householdscouring sponges. Other suitable materials include pervious or permeableflexible and preferably soft sheet materials such as woven and non-wovenfabric and wet-strength paper.

Materials as described in the preceding paragraph allow liquid culturemedium to infiltrate and impregnate their voids and interstices and theyprovide good support and anchorage for the culture medium when it hassolidified.

The supporting means may comprise a base external to the body of culturemedium.

When the supporting means is in part external and in part internal tothe body of culture medium, the part internal to the body of culturemedium constitutes an anchor to hold the culture medium on the part ofthe supporting means external to the culture medium, which latter partmay constitute a base.

Preferably the anchor is held fast or otherwise attached to the base.

Preferably the culturing surface is spaced from a peripheral portion ofthe base by e.g. 1 to 5 mm.

The culturing surface may be circular, rectangular or square.

The culture medium may comprise agar.

The culturing surface may be flat. This enables the culture device to beapplied directly to a flat test area to achieve full contact with thetest area without manipulation of the culture device.

Alternatively the culturing surface may be convex or concave forapplication to particular shapes of test surface.

The anchor may be a disc or plate preferably perforate or in the form ofa grid. It may alternatively consist of a flexible porous or perviousabsorbent material such as described above in respect of the supportingmeans.

The base may be in the form of a container, the peripheral portion ofthe base being a rim of the container.

The term "rim" in relation to the container is intended to encompass anyendless free edge or extremity of the container, which free edge orextremity can surround and define the extent of the body of the culturemedium.

When the base is in the form of a container, the anchor may be a snapfit on a projection upstanding from centre of the container or may beconnected to or integral with a member which is friction fit in thecontainer. Such an anchor is preferably level with the rim of the base.

It may be particularly advantageous for the base to comprise a softflexible or pliable sheet and for the anchor, if present, also to beflexible or pliable. This enables the body of culture medium to bedeformed so that the culture surface can conform to the shape of a testsurface to which it is applied.

In accordance with the invention there is further provided an apparatusfor preparing a culture device, comprising a base for holding a body ofculture medium, and a cover which can cooperate with the base to define,together with the base, a cavity for shaping a body of culture medium,the cavity having a surface provided by the cover for forming theculturing surface of the culture medium, said surface of the cavitybeing spaced from a peripheral portion of the base when the covercooperates with the base and having a defined endless boundary orperimeter so that the body of culture medium shaped in the cavity has acorresponding defined endless boundary or perimeter spaced from theperipheral portion of the base.

The surface of the cavity may comprise an internal surface of the cover.

The base may be in the form of a container, the peripheral portion ofthe base being a rim of the container.

The cover may include means to space said surface of the cavity from therim of the base by a desired distance when the cover is fitted onto thebase.

Said means may comprise a shoulder or abutment of the cover, whichshoulder or abutment is engagable with the rim of the base.

The base may be as described above with reference to the supportingmeans.

The apparatus may include an anchor such as described above, to beembedded in the culture medium.

In accordance with a second, preferred aspect of the invention there isprovided a culture device comprising a strip of fabric (or otherflexible pervious or permeable material), a central portion of which isimpregnated by and supports a body of culture medium providing aculturing surface spaced from the strip and having a defined endlessboundary or perimeter, end portions of the strip, for use inmanipulating the device, being free of the culture medium.

In accordance with the invention there is further provided apparatus forpreparing a culture device, comprising a container and a flexible sheetelement having at least a central portion which is porous, permeable orpervious, first means providing a cavity in a container for receivingthe central portion of the sheet element and for shaping a body ofculture medium formed by solidification or setting of liquid culturemedium, the culture medium when liquid impregnating the central portionof the sheet element whereby the body of the culture medium and thesheet element form a culture device, the central portion supporting theculture medium and maintaining the integrity thereof when the culturemedium is solidified, the body of culture medium having a culturingsurface and the cavity defining side surfaces of said body, which sidesurfaces meet the culturing surface to provide a defined endlessboundary or perimeter of the culturing surface, and second means tomaintain the central portion of the sheet element taut in the cavity andfor allowing end portions of the sheet element to be kept free of theculture medium when the culture medium is solidifying or setting.

Preferably the container has a base which constitutes the base of thecavity.

Preferably side walls of the container form side walls of the cavity.

Preferably the second means not only holds the central portion of thesheet element taut but also forms side walls of the cavity.

There is further provided a method of preparing a culture devicecomprising providing a container and a flexible sheet element having atleast a central portion which is permeable or pervious, locating thecentral portion of the sheet element in a cavity defined in thecontainer with end portions of the sheet element external to the cavity,introducing liquid culture medium into the cavity to impregnate thecentral portion of the sheet element, and, while maintaining endportions of the sheet element free of the culture medium and maintainingthe central portion of the sheet element taut, allowing or causing theculture medium to solidify to form a body of culture medium having afree upper culturing surface or a culturing surface defined by a base ofthe cavity and the cavity defining side surfaces of said body which sidesurfaces meet the culturing surface to provide a defined endlessboundary or perimeter of the culturing surface.

Preferably the sheet element is of woven or non-woven fabric.

Preferably the cavity is defined by side walls and a base of thecontainer and by means which hold the central portion of the sheetelement taut.

Another culture device according to the invention comprises a sheetmember defining a plurality of cavities and a sheet of fabric or otherpervious material extending over the sheet and into the cavities, thebody of culture medium filling at least the bottom portion of eachcavity and impregnating the pervious material, whereby the perviousmaterial in each cavity forms an anchor for the body of culture medium,the base of each cavity defining a culturing surface of the culturemedium, the culturing surface having a defined endless boundary orperimeter.

The invention is further described below by way of example withreference to the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a culture device according to theinvention;

FIG. 2 is a perspective view of apparatus according to the invention forpreparing the culture device of FIG. 1;

FIG. 3 is a vertical sectional view of part of the side walls of theapparatus of FIG. 2;

FIG. 4 is a vertical sectional view of part of the apparatus of FIG. 2showing an anchor; and

FIG. 5A is similar to FIG. 4 but shows an alternative anchor;

FIG. 5B is similar to FIGS. 4 and 5A but shows another alternativeanchor;

FIG. 6 is a perspective view of a container and a lid of a furtherapparatus according to the invention;

FIG. 7 is a plan view of a fabric strip of the apparatus of FIG. 6;

FIG. 8 is a sectional view along a vertical plane of the apparatus ofFIG. 6, culture medium having been added to the apparatus to prepare aculture device according to the invention;

FIG. 9 is a vertical plan view of the culture device of FIG. 8 or FIG.10,

FIG. 10 is similar to FIG. 8 but shows a modification of the apparatus;

FIG. 11 shows another embodiment of the invention; and

FIG. 12 shows a modification of the embodiment of FIG. 11.

Referring to the drawings there is shown a circular culture device 1comprising a base or container 2 which holds a body of culture medium20. The base 2 has a bottom wall 3 and a side wall 4. The side wall 4has a rim 5. The culture medium 20 protrudes from the base 2 and has asmooth, flat surface 6 ("the culturing surface") raised above the rim 5by a distance of 2 mm.

A side surface 7 of the culture medium 20 extends upwardly from the rim5 of the base 2 to the culturing surface 6. The culturing surface 6 andthe side surface 7 meet at an angle of 90° to provide a preciselydefined endless boundary or perimeter 6a of the culturing surface. Thisdefined perimeter enables the surface area of the culturing surface 6 tobe precisely determined.

The internal diameter of the base 2 is selected to provide apredetermined surface area of the culturing surface 6.

The base 2 may be provided, as shown in FIG. 4, with an anchorcomprising a thin disc 8 which is on the same horizontal plane as therim 5 of the base 2. The disc 8 is a snap fit on a post 9. The post 9 isintegrally formed with the base 2 and projects upwardly from the bottomwall 3 of the base. The diameter of the disc 8 is less than the internaldiameter of the base 2. The disc 8 is preferably perforate. The disc 8serves to hold and support the culturing medium.

FIG. 5A shows an alternative anchor. The anchor comprises a perforatedisc 8 integrally formed with a depending peripheral side wall or skirt8A which can fit within the base 2 and frictionally engage the side wall4 of the base. (FIG. 5 shows a space between the side walls 4 and 8Amerely for clarity of illustration).

The culture device 1 further includes a lid or cover 10 which is a closefit onto the base part 2 to define, together with the base part 2, acavity 11. The cover 10, although close fitting on the base 2, is nottight fitting and accordingly can be readily slipped onto the base 2 andeasily removed.

The cover 10 has a top wall 12 and a side wall 13. These walls providerespectively an internal flat smooth top surface 14 and a cylindricalinternal side surface 15. These surfaces meet at an angle of 90°.

The side wall 13 of the cover 10 is provided with an abutment orshoulder 16.

The side wall 13 of the cover 10 has an internal lip 17 below theabutment or shoulder 16. The lip 17 can cooperate with a correspondingexternal lip 18 on the side wall 4 of the base 2.

The cover 10 can be fitted into the base 2 with the shoulder 16 restingon the rim 5 so that the base is fully closed and the surface 14 of thecover is separated from the rim 5 of the base 2 by a desired distance(preferably about 2 mm). Alternatively the cover 10 can be fitted ontothe base 2 with the lip 17 resting on the lip 18 so that shoulder 16 isheld above the rim 5.

In order to prepare the culture device 1, a culture medium in liquidform, e.g. melted agar, is introduced into the cover 10. This can becarried out by inverting the cover 10 and pouring the culture mediumdirectly into the cover and then fitting the base 2 onto the cover or bypouring the culture medium into the base 2 and then fitting the coveronto the base and inverting the base 2 and the cover 10 together totransfer the culture medium into the cover. The culture medium is thenallowed to cool thereby to set or solidify to form the body 20 ofculture medium. The amount of culture medium must be such as to morethan fill the cavity 11 from the surface 14 of the cover 10 to the rim 5of the base 2. If the base 2 is provided with the anchor 8, then theanchor becomes embedded in the solidified culture medium and holds theculture medium firmly in place. The surface 14 of the cover shapes theculturing surface 6 of the culture medium as the culture mediumsolidifies. Similarly the surface 15 of the cover shapes the sidesurface 7 of the culture medium.

The cover 10 can be removed for inspection of the solidified culturemedium or for use of the culture device. Preferably the cover 10 is kepton the base 2 until the culture device 1 is to be used in order toprotect the culture medium from contamination. If desired the cover 10can be replaced on the base 2 without touching the surface of theculture medium by resting the lip 17 on the lip 18.

In use of the culture device i, the cover 10 is removed and theculturing surface 6 is pressed directly against a test surface totransfer micro-organisms to the culturing surface 6 from the testsurface. The surface 6 is then removed from the test surface and themicro-organisms transferred to the surface 6 are allowed to multiplyinto visible colonies. The number of colonies corresponds to the numberof micro-organisms transferred from the test surface to the surface 6.Since the area of the surface 6 is precisely determinable, the number ofmicro-organisms transferred from the test surface to the surface 6 perunit area of the test surface can be precisely determined.

The culture device 1 may be round (as shown) or square in plan. It ispreferred that the base 2 and the cover 10 are round for convenience,versatility and ease of manipulation. The base part 2 and the cover 10may be made of clear transparent material, such as polystyrene, whichlends itself to fabrication and can withstand sterilizing temperaturesor gamma radiation.

The perforated disc or plate 8 forming the anchor in FIG. 5A may bereplaced, as shown in FIG. 5B, by porous or pervious material such asopen cell sponge or foam or a reticulated structure, such as that usedin household scouring sponges. The anchor 8 may be covered by fabric,towelling, or wet strength paper secured to the anchor. Alternativelythe anchor itself could be made of fabric or wet strength paper,towelling, sponge or other materials as discussed above.

Reference is now made to FIGS. 6 to 10.

Apparatus for preparing a culture device comprises a rectangularparallel-pipedal open-topper container 200, a lid or cover 202 for thecontainer and a strip 204 of woven or non-woven fabric.

The width of the strip matches the internal width of the container 200.The length of the strip is somewhat greater than the total of theinternal length of the container plus twice the internal height of thecontainer. Spring clips 206, as shown in FIG. 8, may be provided to holdthe strip 204 in the container 200 with a central portion 204' of thestrip held taut between the ends of the container and in contact withthe base of the container and with end portions 204" of the stripextending over end walls of the container.

The clips 206 have limbs 206' which are sufficiently long to press thecentral portion 204' of the strip 204 into close contact with the baseof the container 200.

In use of the apparatus the strip 204 is arranged as shown in FIG. 8,the strip being held taut between the clips 206 and pressed against thebase of the container 200. Then liquid culture medium is poured into thecontainer. The culture medium is spread out over the fabric strip in alayer 212 and solidifies to form a body of culture medium 212 supportedby and impregnating the fabric.

The upper horizontal surface of the solidified body 212 of culturemedium constitutes a culturing surface. The side walls of the container200 and the limbs 206' of the clips 206 define side surfaces of the bodyof culture medium and the side walls of the container 200 also defineside surfaces of the body 212 of culture medium. These side surfacesmeet the culture surface at 90° and thus the culturing surface has adefined endless boundary or perimeter.

A lid 202 may be placed on the container 200 to protect the body 212 ofculture medium from contamination.

The fabric strip with the solidified body 212 of culture mediumconstitutes a culture device. In use of the culture device the device isremoved from the container and manipulated by means of the end portions204" of the fabric strip.

The culture device may be used in like manner to the culture devicedescribed above. After application of the culturing surface to a testsurface the culture device may be replaced in the container 200 to allowincubation of microorganisms on the culturing surface. The lid 202 maybe used to prevent contamination of the culturing surface duringincubation of the microorganisms.

It will be appreciated that because the fabric strip 204 is flexible thedevice can be used in conjunction with test surfaces which may be flat,curved or uneven, the body of culture medium and the fabric stripaccommodating themselves to the shapes of such test surfaces.

The strip 204 may be of wet strength paper instead of woven or non-wovefabric.

The strip 204 may be temporarily stuck to the end walls and base of thecontainer 200 by adhesive thereby obviating the use of the clips 206.

FIG. 10 shows a modification of the apparatus shown in FIG. 8.

Referring to FIG. 10, the limbs 206' of the clips 206 are shorter sothat the central portion 204' of the strip 204 when held taut betweenthe ends of the container 200 is spaced from the base of the container.The culture medium when set impregnates the central portion 204' of thestrip 204 but has a layer between the strip and the base of thecontainer. The lower surface of the set culture medium constitutes aculturing surface, which is smoother than the culturing surface providedby use of the apparatus shown in FIG. 8.

FIG. 11 shows a further embodiment of the invention.

Referring to FIG. 11, a sheet 300 of clear transparent plastic (e.g.polystyrene) is formed to provide a plurality of blisters or cavities302, each having a cylindrical side wall which meets the base of thecavity at 90°. A piece of fabric 304 is laid over the plastic so as tohang into each cavity. The fabric 304 hanging into the cavity may have apiece of sponge attached to it. A piece of sponge 310 is shown in cavity302 in FIG. 11. The culture medium is then poured over the fabric andpenetrates through the fabric to fill each cavity. The culture medium isallowed to set. The resulting solidified body 306 of culture medium ineach cavity forms a culture device, the culture medium impregnating thefabric/sponge which forms an anchor for the medium. A sheet of aluminiumfoil 308 may be laid over the fabric to shield the culture devices fromcontamination. A suitable plastic sheet 312 may be added to protect thealuminium foil.

It will be appreciated that the base of each cavity defines a culturingsurface of the body of culture medium, the culture surface having adefined endless boundary or perimeter.

FIG. 12 shows a modification of the embodiment of FIG. 11. As shown inFIG. 12, the piece of fabric 304 extends down the sides of each cavityand across each cavity, adjacent/along its base. The upper horizontalsurface of the solidified body of culture medium constitutes theculturing surface.

Each culture device may be individually removed from its cavity for usewhen required.

It will be further appreciated that the aluminium foil may be firmlyadhered to the fabric and solidified culture medium to provide anassembly in which the culture devices are hermetically sealed. Theassembly may be provided with perforations between the culture devicesso that the portions of the assembly, each containing one culturedevice, can be readily separated from the remainder of the assembly.When the aluminium foil is removed from such a separated portion of theassembly, the aluminium foil can then be removed from that portion andthe culture device lifted out of the cavity. After completion ofsampling the culture device can be placed with the culture surfaceupward on the separated portion of the plastic sheet. The separatedportion of the cavity is used to cover the culture device and the twoparts are stapled together for incubation.

The cavity 302 may be round, as shown, or square or rectangular.

I claim:
 1. A culture device comprising a solid body of culture medium and supporting means for maintaining the integrity of the body of culture medium, the culture medium providing a culturing surface having an endless boundary or perimeter, the body of culture medium protruding from and the culturing surface being spaced from any aforesaid means disposed externally of the body of culture medium, the endless boundary or perimeter being defined by a side surface or contiguous side surfaces of the culture medium, which side surface or surfaces meet the culturing surface abruptly along an endless line or endless series of lines at an angle substantially differing from 180° so that the boundary or perimeter is defined, the supporting means being partly internal of and partly external to the body of culture medium.
 2. A culture device according to claim 1, wherein the supporting means at least in part is flexible or pliable to allow the culture medium to deform to accommodate to the shape of a test area to which the culture medium is applied.
 3. A culture device according to claim 1, wherein the supporting means comprises porous, pervious or permeable material impregnated with the culture medium.
 4. A culture device according to claim 3, wherein the porous, pervious or permeable material comprises open cell sponge or foam or material having a three-dimensional reticulated structure.
 5. A culture device according to claim 1, wherein the culturing surface is spaced from a peripheral portion of the supporting means external to the culture medium by 1 to 5 mm.
 6. A culture device according to claim 3, wherein the disc or plate is perforate or in the form of a grid.
 7. A culture device according to claim 1, wherein the supporting means comprises a base external to the body of culture medium and an anchor internal of the body of culture medium and the anchor is held fast or otherwise attached to the base.
 8. A culture device according to claim 1, wherein the supporting means comprises a strip of fabric or other flexible porous, pervious or permeable material, a central portion of which is impregnated by and supports the body of culture medium providing the culturing surface spaced from the strip and having the defined endless boundary or perimeter, end portions of the strip, for use in manipulating the device, being free of the culture medium.
 9. Apparatus for preparing a culture device, comprising a container and a flexible sheet element having at least a central portion which is porous, permeable or pervious, a cavity, being provided in the container for receiving the central portion of the sheet element and for shaping a body of culture medium formed by solidification or setting of liquid culture medium in the cavity, the culture medium when liquid impregnating the central portion of the sheet element whereby the body of the culture medium and the sheet element form a culture device, the central portion supporting the culture medium and maintaining the integrity thereof when the culture medium is solidified, the body of culture medium having a culturing surface and the cavity defining side surfaces of the body which meet the culturing surface abruptly to define an endless boundary, or perimeter of the culturing surface and removable means for defining side walls of the cavity and for maintaining the central portion of the sheet element taut in the cavity and for allowing end portions of the sheet element to be kept free of the culture medium when the culture medium is solidifying or setting, said means forming walls of the cavity.
 10. Apparatus according to claim 9, wherein side walls of the container form side walls of the cavity.
 11. A method of preparing a culture device comprising providing a container and a flexible sheet element having at least a central portion which is porous, permeable or pervious, locating the central portion of the sheet element in a cavity defined in the container with end portions of the sheet element external to the cavity, introducing liquid culture medium into the cavity to impregnate the central portion of the sheet element, and, while maintaining end portions of the sheet element free of the culture medium and maintaining the central portion of the sheet element taut, allowing or causing the culture medium to solidify to form a body of culture medium having a free upper culturing surface or a culturing surface defined by a base of the cavity and the cavity defining side surfaces of said body which side surfaces meet the culturing surface to provide a defined endless boundary or perimeter of the culturing surface.
 12. A method according to claim 11, wherein the sheet element is of woven or non-woven fabric.
 13. A method according to claim 11, wherein the cavity is defined by side walls and a base of the container and by means which hold the central portion of the sheet element taut.
 14. A culture device comprising a sheet member defining a plurality of cavities and a sheet of fabric or other pervious material extending over the sheet and into the cavities, the body of culture medium filling at least the bottom portion of each cavity and impregnating the pervious material, whereby the pervious material in each cavity forms an anchor for the body of culture medium, the base of each cavity defining a culturing surface of the culture medium, the culturing surface having a defined endless boundary or perimeter.
 15. Apparatus for preparing a culture device, comprising a base for holding a body of culture medium and a cover which can cooperate with the base to define, together with the base, a cavity for shaping a body of culture medium, and supporting means at least partly within the cavity and for maintaining the integrity of the body of culture medium, the cavity having a surface provided by the cover for forming a culturing surface of the body of culture medium, said surface of the cavity being spaced from a peripheral portion of the base when the cover cooperates with the base and having an endless boundary or perimeter, the endless boundary or perimeter being defined by a side surface or contiguous side surfaces of the cavity, which latter surface or surfaces meet the first-mentioned surface of the cavity abruptly along an endless line or series of lines at an angle substantially differing from 180° so that the boundary or perimeter is sharply defined, whereby the body of culture medium shaped in the cavity has an endless boundary or perimeter spaced from the peripheral portion of the base.
 16. Apparatus according to claim 15, wherein the supporting means at least in part is flexible or pliable to allow the culture medium to deform to accommodate to the shape of a test area to which the culture medium is applied.
 17. A method of preparing a culture device comprising inverting the cover of the apparatus according to claim 15, introducing liquid culture medium into the inverted cover to fill the cover at least up to the level of the peripheral portion of the base when the cover cooperates with the base and then effecting setting or solidification of the culture medium with the base inverted and fitted to the inverted cover.
 18. A culture device comprising a solid body of culture medium and supporting means for maintaining the integrity of the body of culture medium, the culture medium providing a culturing surface having an endless boundary or perimeter, the body of culture medium protruding from and the culturing surface being spaced from any aforesaid means disposed externally of the body of culture medium, the endless boundary or perimeter being defined by a side surface or contiguous side surfaces of the culture medium, which side surface or surfaces meet the culturing surface abruptly along an endless line or endless series of lines at an angle substantially differing from 180° so that the boundary or perimeter is defined, the supporting means being at least partly internal of the body of culture medium and comprising woven or non-woven fabric or wet strength paper impregnated with the culture medium.
 19. A culture device according to claim 18, wherein the side surface or surfaces meet the culturing surface along an endless line or series of lines at an angle of 90°.
 20. A culture device according to claim 18, wherein the supporting means is partly external to the body of culture medium.
 21. A culture device according to claim 18, wherein the supporting means comprises a base external to the body of culture medium and an anchor internal of the body of culture medium and the anchor is held fast or otherwise attached to the base.
 22. A culture device according to claim 18, wherein the supporting means comprises a strip of fabric or other flexible porous, pervious or permeable material, a central portion of which is impregnated by and supports the body of culture medium providing the culturing surface spaced from the strip and having the defined endless boundary or perimeter, end portions of the strip, for use in manipulating the device, being free of the culture medium. 